RU2818534C1 - Method of producing cast iron grinding bodies - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to production of cast iron articles, in particular, to production of cast iron grinding bodies (balls and cylinders), and can be used for recycling of copper smelting production wastes. Method involves iron smelting using a charge for pellets containing a mixture of copper smelting production wastes, containing copper 0.7–2.4 wt.%, and carbonaceous reducing agent. Pellets are made from the obtained mass, which are dried and fired in a reducing medium to obtain metallized pellets, which are used when loading charge into arc furnace and its melting with production of cast iron. Cast iron is poured into molds to produce grinding bodies. Mixture of granulated slag with maximum grain size of 1.25 mm and sludge from flotation of crystallized ground slag containing 40–70 wt.% of granulated slag is used as copper smelting wastes.

EFFECT: enabling expansion of the raw material base of ferrous metallurgy when producing cast iron grinding bodies due to use in their production of both old (stale) dumps and slags of current production, recycling copper-smelting production wastes.

1 cl, 2 tbl, 1 ex

Description

The invention relates to the production of cast iron products, in particular to the production of cast iron grinding media (balls and cylinders), and can be used for the disposal of copper smelting waste.

The problem is this. A potential raw material base for ferrous metallurgy is waste from the copper industry: slag, which, depending on the technology adopted at the plants, contains from 0.3 to 3% copper and up to 40% iron. The dumps of enterprises contain 2 types of slag with different copper content: granular, produced using outdated technology, and sludge obtained from ground slag crystallized by slow cooling, subjected to foam flotation for additional extraction of copper residues. Millions of tons of this waste are stored in dumps, which occupy large areas and create environmental problems.

One way to solve the problem is to use slag to produce cast iron and then produce grinding media.

The increased sulfur content (up to 1%) in cast iron made from copper slag does not reduce the performance characteristics of grinding media, and the presence of copper (0.3 - 1%), which is a natural alloying additive, significantly improves its mechanical properties (Mikhailov A.M., Bauman B. V., Blagov B.N. “Foundry”, “Mechanical Engineering”, 1987).

The composition of the charge for producing cast iron grinding media is known, where waste from the production of stone-cast products from copper smelting slag is used as an alloying additive in an amount of 5 - 15% by weight of the charge /p. RF No. 2016077, IPC S21S1/08, application. 04/03/1992, publ. 07/15/1994/ The composition of the resulting cast iron is as follows: wt. %: 3.11-3.9 C; 0.11-0.8 Si; 0.02-0.8 Mn; 0.9-2.1 Cu, iron - the rest.

The disadvantage of the known composition is that up to 15% of waste from the melting of copper slag is used as a copper-containing additive, and the remaining 85% of the charge is expensive pig iron. In addition, stone casting from copper slag has not found industrial application.

The closest in technical essence to the proposed invention is the composition of the charge for the preparation of metallized pellets for the production of grinding media, described in the method for producing cast iron grinding media, presented in clause RF 2634535, IPC S21C 1/08, appl. 2016.08.23, publ. 2017.10.31, including copper smelting slag with a copper content of 0.7 to 2.4% and a carbon reducing agent as starting materials. The wording “copper smelting slag” in the formula of the prototype patent does not contain information about the composition of the slag and method of its preparation, which does not allow it to be effectively used for the production of metallized pellets for the production of grinding media.

The technical task and result of the invention is to expand the raw material base of ferrous metallurgy in the production of cast iron grinding media through the use in their production of both old (stale) dumps and slags from current production, and the recycling of copper smelting waste.

The technical problem is achieved due to the fact that the method for producing cast iron grinding media includes smelting cast iron using a charge for pellets containing a mixture of copper smelting waste containing copper 0.7-2.4 wt.%, and a carbon reducing agent, Moreover, pellets are made from the resulting mass, which are dried and fired in a reducing environment to obtain metallized pellets, which are used when loading the charge into an arc furnace and melting it to produce cast iron, then the cast iron is poured into molds to obtain grinding media, according to the invention, as Copper smelting waste uses a mixture of granulated slag with a maximum grain size of 1.25 mm and sludge from the flotation of crystallized ground slag containing 40-70 wt.% granulated slag.

It is known that there are two types of copper smelting waste slag: granulated slag and slag sludge, which differ in the method of production, phase and granulometric composition.

Froth flotation sludge is a highly dispersed powder composed of crystallized (by slow cooling) and wet-ground slag. The sludge is characterized by a high grinding fineness (the content of particles of a class less than 0.05 mm is 94 wt.% with a high specific surface area).

Granulated slag from copper production is coarse sand almost entirely composed of glass (up to 98 wt.%).

It is known that in the production of pellets, the granulometric composition of the charge has a great influence on their quality and technical and economic characteristics (Maerchak Sh. Production of pellets, M. "Metallurgy", 1982). Granulated slag practically does not contain fine fractions (Table 1), which are necessary to ensure the cohesion of the resulting pellets. In addition, the slag almost entirely (up to 98 wt. %) consists of glass, its grains have a smooth surface. Reduced surface tension is the reason for the poor water-holding capacity of granular slags.

It has been established that the poor clumping properties of the charge with granulated copper production slag without the addition of fine fractions does not allow the production of pellets for iron reduction. The second feature of granulated slag made of dense glass is the fragility of the grains, caused by internal stress resulting from thermal shock during water granulation. Slag glass is penetrated by a network of thin cracks, which was established by high-resolution electron microscope studies. Stress centers are sulfide particles evenly distributed throughout the glass mass. Even small efforts, heating and cooling during drying lead to the destruction of large grains. Avalanche-like destruction, especially under shock and thermal loads, is typical for grains larger than 1.25 mm. Smaller grains have high strength and abrasiveness and are difficult to grind. The energy intensity of fine grinding of copper slag, compared to blast furnace slag, is 40 wt. % higher.

The most effective and economical is grinding to a boundary grain of 1.25 mm in impact crushers (rotary, hammer, etc.). Further grinding of slag glass grains in order to obtain a sufficient amount of fine fractions to ensure the clumping of the charge for pellets is energy-intensive and economically unprofitable. It has been established experimentally (when tested in a rotating drum) that dried pellets with granulated slag that have not been crushed along a boundary grain of 1.25 mm have a shedding of the surface layer, which results in high losses (spills) during handling and transportation.

The influence of the degree of grinding of the charge during the production of pellets is ambiguous. With an increase in the specific surface of the charge to a certain value, the quality indicators of the charge and pellets: clumping, water content, strength of raw pellets, strength of dried pellets improve. With a further increase in the specific surface area, the water content increases, which leads to an increase in energy consumption for drying.

Copper smelting sludge has a relatively high specific surface area (about 1360 cm ² /g). It has been experimentally established that with such a specific surface area, its use without a coarsening additive is ineffective, because Due to high moisture content, obtaining high-quality pellets requires high moisture content of the charge, which leads to extended drying time, reduced productivity and increased energy intensity. Insufficient moisture content of the charge leads to a decrease in the strength of raw and dried pellets.

The proposed combination, within the specified boundaries, of relatively large grains that create the “framework” of the pellet and a fine fraction - sludge, which improves the cohesion of the particles, ensures the achievement of the required quality indicators: strength of wet pellets, strength of dry pellets, and efficiency.

The limits for the content of granulated slag in the mixture are determined by the following. When the upper limit of the granulated slag content in the charge is exceeded and the lower limit is reduced, the coherence of the particles and the strength of the raw and dried pellets deteriorate (Table 2). The use of a mixture of two types of slag in the charge in the specified ratio makes it possible to expand the raw material base of ferrous metallurgy by involving both old (stale) dumps and slags of current production into production, and to improve the quality of pellets.

The inventive method is novel in comparison with the prototype due to the presence of such distinctive features as the use in the charge of a mixture of two types of copper production slag, with a quantitative content of components: 40-70 wt. % of granulated slag by weight of the mixture, grain composition of granulated slag: fractions less than 1.25 mm, which together ensure the achievement of the desired result.

The proposed method for producing cast iron using a charge of the specified composition for pellets for smelting cast iron in the manufacture of grinding media can be widely used for recycling waste from copper smelters (current production and old dumps), in particular in the Southern and Middle Urals, Taimyr, Kazakhstan and other regions .

The implementation of the proposed composition of the charge used in the proposed method is as follows.

Take two types of copper slag with a copper content of 0.7-2.4 wt. %: sludge and granulated, pre-crushed to a size of minus 1.25 mm, mixed with a carbon-containing reducing agent (coal, coke), a binder (liquid glass, bentonite), water, pellets are made on a drum or disc granulator, which are dried. From the resulting pellets, cast iron is obtained by solid-phase reduction of iron and subsequent smelting, which is poured into molds to produce grinding bodies (balls).

An example of the practical implementation of the claimed charge in the method of producing cast iron grinding media

Source materials: a mixture including sludge from the flotation tailings of the Karabash copper smelter containing 0.7 wt. % copper and granulated slag from old dumps of the same plant with a copper content of 0.9 wt. %, previously crushed in a hammer crusher to a fraction of minus 1.25 mm, reducing agent: coal, crushed in a disk mill to a fraction of minus 1 mm, in an amount of 20 wt. % by weight of slag, binder - ground bentonite, in an amount of 1 wt. % by weight of the charge. Granulated slag, sludge and coal were dried to constant weight and mixed with a binder. The amount of binder in the mixture was 0.9 wt. % by weight of the charge. The amount of granulated slag in a mixture of two types of slag was, wt. % from 40 to 70. Additionally, for comparison, charge compositions containing granulated slag, wt. % 25-35 and 75-80.

The mixture of these starting materials was then mixed with water to a moisture content of 10% for 10 minutes for the production of pellets, loaded into a laboratory drum granulator with a diameter of 340 mm, and granulated. The strength of raw pellets with a diameter of 14-16 mm was determined by dropping them (from a height of 50 cm) onto a cast iron plate. The raw pellets were dried in an oven at a temperature of 120 degrees. The crushing strength of the dried pellets was determined.

As shown by the test results of pellets (Table 2), high strength indicators are achieved with a content of 40-70 wt. % sludge in a slag mixture. When the granulated slag content decreases to less than 40 wt. % and an increase of more than 70 wt. % strength of raw and dried pellets decreases.

Dried pellets of optimal composition were subjected to metallization by firing in a reducing environment, after which cast iron was smelted in an arc furnace. The smelted metal was melted in an induction furnace and poured into a cast iron split mold. As a result, samples of cast iron balls with a diameter of 40 mm were obtained, corresponding to GOST 7524-89 “Steel grinding balls” and KR ST 2310-2013 “Cast cast iron grinding balls”.

Table 1. Granulometric composition of the original and crushed slag Name of material Residue on sieve with hole diameter, mm 5 2.5 1.25 0.63 0.32 0.1 bottom Initial slag 3.5 22.1 29.7 32.2 7.58 1.3 3.7 Crushed slag - - - 61.1 24.8 9.1 5.1

Table 2. Dependence of the strength of pellets on the content of granulated slag in the mixture Pellets strength Content of granulated slag in the mixture 25 thirty 35 40 50 60 70 75 80 Raw (number of drops) 7.6 8.1 11.3 13.4 14.9 14.3 12.8 6.2 4.7 Dry (kg/pellet) 11.8 12.1 16 29.7 56.3 54.6 31.2 17.1 9.9

Thus, the use of the proposed charge composition ensures the production of pellets of the required quality (Table 2) and the smelting of cast iron from them for grinding media that meet regulatory requirements.

Claims (1)

A method for producing cast iron grinding media, including smelting cast iron using a charge for pellets containing a mixture of copper smelting waste containing 0.7-2.4 wt.% copper, and a carbon reducing agent, and pellets are made from the resulting mass, which dried and fired in a reducing environment to obtain metallized pellets, which are used when loading the charge into an arc furnace and melting it to produce cast iron, then the cast iron is poured into molds to obtain grinding media, characterized in that a mixture of granulated slag with maximum grain size of 1.25 mm and sludge from flotation of crystallized ground slag containing 40-70 wt.% granulated slag.